My U.S. Pat. No. 4,526,091 for an "Adjustable Roof Jack," issued on July 2, 1985, describes and cIaims an adjustable roof jack which may be used to connect a roof mounted air handler to an interior air duct through a roof of a building, wherein the roof pitch may be within a wide range of angles from the horizontal; from horizontal to approximately a 5/12 slope. Because the jack there described may accommodate such a wide range of roof slopes, it has enjoyed a substantial degree of commercial success.
In some parts of the world, it is feasible to utilize evaporative coolers in lieu of mechanical air conditioning systems which are more expensive to operate. In many of these locations, it may be feasible to utilize an evaporative cooler in those seasons of the year when there is a low ambient humidity; but when the percentage of humidity rises, it is advantageous to switch to evaporator-compressor-condenser (refrigeration) systems. Therefore, it is the practice in some climates to use what has come to be known as "piggyback" systems.
In such a system, facilities are provided so that either a refrigeration unit or an evaporative cooler may be utilized as the cooling source, both units being roof mounted and capable of being switched into a common supply duct to a building duct system, below. Generally, this switching is accomplished by inserting a sheet metal plate into the duct system at an appropriate point (or points) to isolate the air outlet of the unused unit.
Because roof mounted refrigeration units are frequently installed so that cold air is delivered from one vertical side thereof, a ninety degree sheet metal duct bend is employed to carry the air downward to a roof level connection with the interior duct system. While the radius of a given air conditioning supply bend is subject to some variation, the majority of them use a bend which is designated in the industry as a 11/2 inch per foot bend.
It is common practice to gain access to the common duct system for an add-on evaporative cooling system by cutting a hole in the bend of the air conditioning supply duct and custom manufacturing a sheet metal duct attachment thereto into which the outlet of the evaporative cooler is led by means of the specially fabricated sheet metal duct work. A metal slide is then employed to block the outlet of the evaporative cooler during those seasons when the cooler is not in use. However, because it is important that the evaporative cooler be mounted parallel to the horizon so that the water in the sump is level, each of these applications must be designed and fabricated to fit the particular configuration encountered in each retrofit job.